1. Technical Field
The present invention relates to a self-sealing unit, a liquid ejecting head unit and a liquid ejecting apparatus, and, particularly, the present invention is useful when it is applied to the case of opening and closing a liquid supply route by moving a valving element by a film which deflects with fluctuation of pressure in a pressure chamber.
2. Related Art
As a typical example of a liquid ejecting head, for example, an ink ejecting head is known which discharges an ink drop from a nozzle opening by using a pressure which acts on ink in a pressure generating chamber due to displacement of a piezoelectric element. The ink ejecting head according to the related art discharges ink supplied from a liquid source such as an ink cartridge filled with ink, from a nozzle by driving a pressure generator such as a piezoelectric element and a heating element. For example, by inserting an ink supply needle into an ink cartridge, ink in the ink cartridge is introduced to a reservoir, which is a common liquid chamber of the liquid ejecting head, from an introduction hole of the ink supply needle.
Some of ink ejecting heads of this kind are such that is combined with a self-sealing unit provided on a flow path for supplying ink for the ink ejecting head from a liquid supply source, such as an ink cartridge, to constitute an ink ejecting head unit. When a negative pressure occurs inside a reservoir by an ink drop being discharged from a nozzle opening, the self-sealing unit of such an ink ejecting head unit opens a valving element to supply ink from an ink cartridge to the reservoir of the ink ejecting head. Accordingly, the self-sealing unit is a part of a flow path provided with a valving element, and a pressure chamber in which the negative pressure acts is formed in its body in which the ink flow path is formed. The pressure chamber is formed by covering its opening section with a film. Thus, the valving element is pressed by the film deflecting toward the pressure chamber side due to the negative pressure which acts in the pressure chamber, and the valving element moves by the pressing force and opens the flow path.
Japanese Patent No. 3,606,282 discloses, as a related art, a self-sealing unit having such a self-sealing function.
In general, the pressure chamber of the self-sealing unit as described above is round. Accordingly, it is optimal to arrange the valving element at the center of the pressure chamber. However, the actual situation is that the position of the valving element is set eccentrically from the center of the pressure chamber because of the relationship with surrounding members. A film covering the opening section of the pressure chamber is heat-welded at the peripheral part of the opening section on the body of the self-sealing unit in the state of being pressed onto the peripheral part. As a result, there may occur a case where the film of the area corresponding to a part of the pressure chamber which is relatively large due to the eccentrical displacement of the valving element is stretched with a higher tension in comparison with the film of the area corresponding to a relatively small part on the opposite side.
As described above, in the case where the tension of a part of the film is higher than that of other parts, there may occur a case where the valving element cannot be moved by a predetermined negative pressure. Consequently, the valving element does not open sufficiently in this case, and smooth supply of ink to the ink ejecting head is retarded.
Such a problem is not limited to ink ejecting head units. The problem similarly exists in liquid ejecting head units for ejecting liquid other than ink.